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11-26-2022, 11:20 PM   #1
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Sigma 18-35mm f/1.8 DC AF performance

Hello everyone, I am interested in buying the Sigma 18-35mm f/1.8 DC. I read about it on the forums and it seems the AF performance is flaky. Has anyone tried this lens on a Pentax KP?

Thanks.

11-27-2022, 03:32 AM - 1 Like   #2
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Yes. And a K-3. I don't find the autofocus any more flaky than the other Pentax glass I own (DA*300, DA15 Ltd, DA35 Ltd macro, DA*11-18, DFA 100 Macro). The DoF is pretty thin at the wide end so if it's critical, live view is the go if you have a static subject. I almost always use centre point when using autofocus - some user comments seem to indicate this more reliable method. YMMV. It is a big chunk of lens. Beautiful for nightscapes!
11-27-2022, 03:36 AM - 1 Like   #3
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I have this lense, I would say it's quite good performer. It's not the best of best lens in AF speed but not so bed as it's described here on forum. I use it at K1 and K-70. I think this lens limited by bodies... Maybe on K3-III it will be better.
What I do not like at this lens it's coma and astigmatism and CA in astrophotography. I think it should be better for that money... I shoot mostly astrophotography and I'm a bit picky to aberrations.
But in general for APS-C it's best what you can find for Pentax. List of modern limited lenses is short, it's sad.
11-27-2022, 06:22 AM - 1 Like   #4
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QuoteOriginally posted by PardonMyShutterSound Quote
I have this lense, I would say it's quite good performer. It's not the best of best lens in AF speed but not so bed as it's described here on forum. I use it at K1 and K-70. I think this lens limited by bodies... Maybe on K3-III it will be better.
What I do not like at this lens it's coma and astigmatism and CA in astrophotography. I think it should be better for that money... I shoot mostly astrophotography and I'm a bit picky to aberrations.
But in general for APS-C it's best what you can find for Pentax. List of modern limited lenses is short, it's sad.

Yes, the list of modern glass is limited, which lens are you currently using for astrophotography? I have the 12-24 mm f/4 and the old 16-50 SMD lens. I was eyeing the f/1.8 for the extra stop of light.

---------- Post added 11-27-22 at 07:25 AM ----------

QuoteOriginally posted by Grimmus Quote
Yes. And a K-3. I don't find the autofocus any more flaky than the other Pentax glass I own (DA*300, DA15 Ltd, DA35 Ltd macro, DA*11-18, DFA 100 Macro). The DoF is pretty thin at the wide end so if it's critical, live view is the go if you have a static subject. I almost always use centre point when using autofocus - some user comments seem to indicate this more reliable method. YMMV. It is a big chunk of lens. Beautiful for nightscapes!
Thanks, are you happy with the 11-18 DA*? I am planning to get the sigma for night scape and astrophotography. I currently have the 12-24 F/4 and the old 16-50 DA* and I'm looking for something more modern.

11-27-2022, 07:49 AM - 1 Like   #5
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QuoteOriginally posted by nerky774 Quote
Yes, the list of modern glass is limited, which lens are you currently using for astrophotography? I have the 12-24 mm f/4 and the old 16-50 SMD lens. I was eyeing the f/1.8 for the extra stop of light.

---------- Post added 11-27-22 at 07:25 AM ----------



Thanks, are you happy with the 11-18 DA*? I am planning to get the sigma for night scape and astrophotography. I currently have the 12-24 F/4 and the old 16-50 DA* and I'm looking for something more modern.
I'm using Irix 15mm f2.4 and Rokinon 24mm f1.4 and Sigma 18-35, but on FF it usable from 24mm(very small crop needed).
Irix 15mmf2.4 is really good lens for astro. Not the fastest but fast enough and on FF it's wide, maybe even too wide
Rokinon 24mmf1.4 usable from f2.5, probably not best copy...
About sigma I already wrote.
I also own Takumar 200mm F4 in M42 mount. Very flat field, nice star shapes, only CA is makeing a bit of problem and slow f-number. But for its money it's excellent.
Now I'm going to buy again 21mm f1.4 from Irix, with 1st copy I had a bed luck. I'm waiting for clear sky without clouds and moon... To test it...
I would be happy to spend my money for something good for astro(fast and no aberrations) from Pentax. But it's not available in my opinion... They have *85mm f1.4 and *50mm f1.4 need to be stoped down to get good results, but then I don't see a reason to pay so much if they starting to be good from f2.8. For wide field I think there is nothing at all. All those 16-50, 11-18 are f2.8 and you need to stop down them.
11-27-2022, 11:23 AM   #6
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well ...

my experience with DA* 11-18 is very, very positive. My copy is very sharp even at F2,8. But I am not shooting astro ...
11-27-2022, 12:11 PM   #7
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QuoteOriginally posted by cport Quote
my experience with DA* 11-18 is very, very positive. My copy is very sharp even at F2,8. But I am not shooting astro ...
sure, modern lens with cost over $1,000 is good or very good during daytime photography. It would be unforgivable if it wasn't.

11-27-2022, 12:34 PM - 1 Like   #8
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...

So ... if I understand well, there is a problem with DA* 11-18 for astrophotography?


Btw. Zdravim od Ostravy do Budejic
11-27-2022, 01:03 PM   #9
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QuoteOriginally posted by PardonMyShutterSound Quote
I'm using Irix 15mm f2.4 and Rokinon 24mm f1.4 and Sigma 18-35, but on FF it usable from 24mm(very small crop needed).
Irix 15mmf2.4 is really good lens for astro. Not the fastest but fast enough and on FF it's wide, maybe even too wide
Rokinon 24mmf1.4 usable from f2.5, probably not best copy...
About sigma I already wrote.
I also own Takumar 200mm F4 in M42 mount. Very flat field, nice star shapes, only CA is makeing a bit of problem and slow f-number. But for its money it's excellent.
Now I'm going to buy again 21mm f1.4 from Irix, with 1st copy I had a bed luck. I'm waiting for clear sky without clouds and moon... To test it...
I would be happy to spend my money for something good for astro(fast and no aberrations) from Pentax. But it's not available in my opinion... They have *85mm f1.4 and *50mm f1.4 need to be stoped down to get good results, but then I don't see a reason to pay so much if they starting to be good from f2.8. For wide field I think there is nothing at all. All those 16-50, 11-18 are f2.8 and you need to stop down them.
I have the irix on my wishlist. Even with the 1.5 crop from the KP should be nice enough for astro.
11-27-2022, 01:12 PM   #10
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QuoteOriginally posted by nerky774 Quote
Thanks, are you happy with the 11-18 DA*? I am planning to get the sigma for night scape and astrophotography. I currently have the 12-24 F/4 and the old 16-50 DA* and I'm looking for something more modern.
Very happy with it. I have some star 100% crops of the corner and centre in my gallery (also linked from the lens review I posted) but to summarise with respect to nightscapes, there is some elongation of stars in the corner at 11 mm and the star shapes in the corners at the 18 mm end are not perfect so it needs to be stopped down. The centre is good from f2.8 so it is usable depending how critical the corners are for you. For general day use, I can't fault it, cracking! Much better than DA limited options. For nightscapes, the Sigma 18-35 is better, obviously faster, but also better corner star shapes at wider apertures. If you want to see what you are getting with the Sigma, I've uploaded some 100% crops into the Great Astro Lens test thread over in the Astrophotography group (post #64) The Great Astro Lens Test - Astrophotography - PentaxForums.com. Other APS-C users have posted information in that group also, do a search.

Hope this helps
11-27-2022, 02:20 PM - 2 Likes   #11
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QuoteOriginally posted by cport Quote
So ... if I understand well, there is a problem with DA* 11-18 for astrophotography?


Btw. Zdravim od Ostravy do Budejic
For day time it perfect lens.
For astro everything depends from your requirements, if you are fine with aperture 2.8+ and you don't care about star shapes in corners then it's fine, you can crop the image...

If you are more strick to IQ, if you do some prints for sale, then I think it's not the best lens.

BTW, svět je těsný)

---------- Post added 11-27-22 at 02:29 PM ----------

QuoteOriginally posted by nerky774 Quote
I have the irix on my wishlist. Even with the 1.5 crop from the KP should be nice enough for astro.
Irix 15mm f2.4 looks like has no competition at FF for K mount, not only because optical quality.
But other useful staff: sealing, focus lock, infinity calibration on lens, tactile feeling when infinity reached. Last one is really useful.

Today I had time to make few shots with Sigma 18-35mm at Pentax K1. I will share few image examples after I finish editing.
In general for APS-C you will not find any better for K-mount.
12-03-2022, 01:39 AM   #12
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Here is example what you can get with this lens at Pentax K1(usable on FF from 26-35mm), so on crop it will be only better.
Moonset | Captured on Sigma 18-35mm f1.8 on Pentax K1. EXIF:? | Flickr
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